1. Field of the Invention
The present invention relates to a fluorescent luminous tube wherein any desired shape of a getter mirror film is formed by scanning a getter material with a laser beam.
2. Description of the Prior Art
FIG. 6 is a plan view and a cross-sectional view partially, each illustrating a conventional fluorescent luminous tube of a type provided with a ring getter. FIG. 6(a) is a plan view illustrating an anode substrate. FIG. 6(b) is a cross-sectional view illustrating the portion taken along the line Y1—Y1 of FIG. 6(a). FIG. 6(c) is a plan view illustrating a getter material and a getter mirror film.
Referring to FIGS. 6(a), 6(b) and 6(c), numeral 51 represents an anode substrate formed of an insulating material such as glass, ceramic, or the like. Numeral 52 represents a front substrate such as glass. Numerals 531 to 533 represent side members such as glass. Letter A represents an anode electrode on which a fluorescent substance is coated. Numeral 611 represents a getter material. Numeral 612 represents an iron-made ring container plated with nickel. Numeral 521 represents a display area. The ring getter is formed of the ring container 612 and the getter material 611. The ring container 612 is mounted on the support 613 which is firmly fixed to the push plate 614 mounted on the anode substrate 51.
When the ring container 612 is heated by a radio-frequency induction heating method, the getter material 611 evaporates and spatters out in the directions of the arrows to form a getter mirror film 62 on the inner surface of the front substrate 52. The getter mirror film 62 must be formed on a limited area outside the display area 521 on the front substrate 52.
FIG. 6(c) shows the relationship between the ring getter 611 and the getter mirror film 62. The diagram is shown so as to superpose the getter material 611 on the getter mirror film 62. The size of the getter mirror film 62 depends on the diameter of the getter material 611 and the distance between the aperture of the ring container 611 and the inner surface of the front substrate 52 (because a getter mirror film is formed while the getter material is expanding). The shape of the getter mirror film 62 depends on the shape of the ring getter material 611.
FIG. 7 shows an example of a getter of a type, which is heated by a direct conduction resistance heating method. Like numerals are attached to the same elements as those in FIG. 6.
Referring to FIGS. 7(a), 7(b) and 7(c), numeral 711 represents a getter material, 712 represents a linear container which generates heat by conduction, and 713 represents a support/conduction lead member. The linear container 712 is firmly fixed to the support/conduction lead member 713. The support/conduction lead member 713 is firmly fixed to the anode substrate 51. Both the ends of the support/conduction lead member 713 are pinched between the side member 532 and the anode substrate 51 and are led out externally. Each of the lead-out portions acts as a terminal for energizing the linear container 712.
When an electric current flows via the support/conduction lead members 713, the linear container 712 is heated because of the resistance of the container itself. Thus, the getter material 711 evaporates and spatters in the directions of the arrows so that the getter mirror film 72 is formed on the inner surface of the front substrate 52.
In this operation, the getter mirror film 72 becomes oval, as shown in FIG. 7(c). The size of the getter mirror film 72 depends on the size of the getter material 711 and the distance between the getter material 711 and the inner surface of the front substrate 52, as shown in FIG. 6. The shape of the getter mirror film 72 depends on the shape of the getter material 711.
In the structure shown in FIGS. 6 and 7, the size and shape of the getter mirror film is uniquely determined automatically by the size and shape of the getter. For that reason, the size and shape of the getter mirror film cannot be controlled arbitrarily. Namely, provided that the distance between a getter and the front substrate is fixed, the size of the getter mirror film depends on the size of the getter. In accordance with the size of the place where a getter mirror film is formed, a getter having the size suitable for the place must be selected. Moreover, since the size of a getter mirror film depends on the size of a getter, the getter mirror film becomes circular or oval even if the place on which the getter mirror film is formed is, for example, rectangular. Hence, when a circular getter mirror film is formed at a rectangular place, the corners of the rectangular place become dead spaces. The getter mirror film must be formed outside the display area of the front substrate. However, when the position of a getter is shifted three-dimensionally, the getter mirror film may be formed inside the display area. Such a displacement results in a defective fluorescent luminous tube. For that reason, mounting an envelope filled with a getter material requires a high precision and takes much time for positioning. To mount the envelope with low precision, the position of a getter must be separated sufficiently from the display area, so that the dead space becomes larger.